Multi-layer optical disc and its manufacturing method

ABSTRACT

A kind of optical disc consists of the first layer, the second layer and the in-between layer, which lies between the first layer and the second layer. The first layer with its surface undulant includes material used to record information. The second layer with its surface basically flat includes material used to record information referring to the undulation of the first layer. The method to manufacture this optical disc comprises the steps of forming undulant first layer; forming the in-between layer on the surface of the first layer; and then forming the second layer. The first layer includes material used to record information, and the second layer includes material used to record information referring to the undulation of the first layer.

TECHNICAL FIELD

The present invention relates to an optical disc and its manufacturingmethod, specifically to a multi-layer optical disc and its correspondingmanufacturing method.

TECHNICAL BACKGROUND

With the development of the optical storage technology, there areexisting more and more optical discs for storing (recording) datainformation, such as DVD, VCD, CD, etc. In these optical discs, DVD,VCD, CD, etc. are classified and named according to different standardsspecified for the optical discs. However, the optical discs can also beclassified as the one-recording-layer optical disc and themulti-recording-layer optical disc according to their physicalstructures, and the dual-recording-layer optical disc is the most commonone in the multi-recording-layer ones. Compared with the one-layeroptical disc, the dual-layer optical disc is more complicated not onlyin the physical structure but also in the corresponding manufacturingprocess.

FIG. 5 shows a kind of dual-layer optical disc 5 manufactured using the2P (Photo-Polymerization) process, comprising substrate 510, firstrecording layer 514, in-between layer 515, second recording layer 516and protecting layer 520 in sequence, wherein first pre-recorded groove512 and second pre-recorded groove 513 are formed on substrate 510 andin-between layer 515 respectively. First recording layer 514 and secondrecording layer 516 become undulate along first pre-recorded groove 512and second pre-recorded groove 513 respectively, so that the undulationis used to position the optical head, to trace the address, to controlrotating speed of the optical disc and so on. Both first recording layer514 and second recording layer 516 include many sub-layers, such asfirst dielectric layers, functioning layers, second dielectric layers,metallic reflecting layers (or semi-reflecting layers), etc. (not shownin the drawings).

The above-mentioned first pre-recorded groove 512 and secondpre-recorded groove 513 in dual-layer optical disc 5 are formed bymould-pressed substrate 510 and in-between layer 515 respectively withconventional nickel stamper. If another recording layer is required tobe added on the dual-layer disc 5, the stamper must be used once more,that is, the stamper must be used once more when a new recording layeris required to be added on the optical disc. Therefore, it is obviousthat the manufacturing process becomes complex, the productivity isreduced, and the production cost is increased.

Furthermore, during the multiple mould-pressing processes, it isdifficult to register accurately the positions of the stamper betweenthe preceding mould-pressing and the subsequent mould-pressing, which isliable to cause failures in the mould-pressing processes and reducethroughput.

Moreover, second pre-recorded groove 513 on in-between layer 515 indual-layer optical disc 5 made using 2P process needs to be solidifiedby ultraviolet radiation after being mould-pressed. However, theultraviolet radiation can penetrate neither first recording layer 514including the metallic reflecting layer nor the conventional nickelstamper. Therefore it's difficult to solidify the second pre-recordedgroove on the in-between layer.

In order to solve the problem, the plastic stamper is usually used toreplace the nickel stamper, so that the ultraviolet radiation canpenetrate the stamper and solidify the second pre-recorded groove.However, the plastic stamper has much limited service lifespan and poordemoulding property, so that the throughput is rather low and it is hardto realize the commercialized production.

Therefore, there is a need for an improved optical disc and itsmanufacturing method to avoid the above-mentioned disadvantages.

SUMMARY OF THE INVENTION

An object of the invention is to provide a simply structured opticaldisc.

A further object of the invention is to provide a method formanufacturing the optical discs with the low cost and the simpleprocess.

The object of the invention for solving the technical problems isrealized by implementing the following technical solution. The opticaldisc according to the Invention comprises a first layer, a second layerand an in-between layer between the first layer and the second layer,wherein the surface of the first layer is formed so as to becomeundulate and contains some material used to record the data informationthereon, whereas the surface of the second layer is substantially flatand smooth and contains some material used to record the datainformation thereon with reference to the undulation of the first layer.

The optical disc according to the invention is realized by implementingthe following technical process: forming a first layer with an undulatesurface; forming an in-between layer on the surface of the first layer;and forming a second layer with a substantially flat and smooth surfaceon the in-between layer, wherein the first layer contains some materialused to record the data information thereon, the second layer containssome material used to record the data information thereon with referenceto the undulation of the first layer.

According to the technical solution of the invention, in the opticaldisc of the invention only one layer for recording the data informationbecomes undulate, and other layers for recording the data informationare substantially flat and smooth, with which the in-between layers arecoated directly and respectively, so that it is unnecessary that thestamper must be used once more when a new recording layer is required tobe added on the optical disc, not only saving the stampers, but alsoincreasing the productivity and reducing the production cost.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of the optical disc according to the firstembodiment of the invention;

FIG. 2A, FIG. 2B, FIG. 2C, FIG. 2D and FIG. 2E are the sectional viewsshowing the manufacturing processes of the optical disc according to thefirst embodiment of the invention;

FIG. 3 is a sectional view of the optical disc according to the secondembodied of the invention;

FIG. 4 is a schematic drawing showing the process of recording the datainformation onto the optical disc according to the first embodiment;

FIG. 5 is a sectional view of an optical disc in the prior art.

DETAILED DESCRIPTION OF THE INVENTION

The embodiments of invention will be further described with reference tothe accompanying drawings. FIG. 1 shows an optical disc according to thefirst embodiment of the invention. Optical disc 1 of the embodimentcomprises substrate 110 and protecting layer 120. Substrate 110comprises pre-recorded groove 112 integrally formed by mould-pressing.The surface of pre-recorded groove 112 on substrate 110 is coated withfirst recording layer 114, and first recording layer 114 is formed tobecome undulate along pre-recorded groove 112 to position the opticalhead, to trace the address, to control the rotating speed of the opticaldisc and so on by the undulation. In-between layer 115 is providedfurther on first recording layer 114. In-between layer 115 is atransparent glutinous layer, so that it will substantially fill andlevel up the undulation on first recording layer 114. The top surface ofin-between layer 115 is coated with second recording layer 116 having asubstantially flat and smooth surface, so that positioning the opticalhead, tracing the address and controlling the rotating speed of theoptical disc should be implemented with reference to first recordinglayer 114 when the data information is recorded onto second recordinglayer 115. Protecting layer 120 covers second recording layer 116.

Both first recording layer 114 and second recording layer 116 of opticaldisc 1 include many sub-layers, such as first dielectric layers,functioning layers, second dielectric layers, reflecting layer s (orsemi-reflecting layer s), etc., the same structure as the recordinglayer of optical disc in the prior art, thus not shown in the drawings.

In these structures of respective layers of optical disc 1, substrate110 is generally formed of polycarbonate, or of glass, PMMA or otherorganic material.

In the respective sub-layers contained in first recording layer 114 andsecond recording layer 116, the reflecting layer (or the semi-reflectinglayer) can be formed of gold, silver, aluminum, etc.; the dielectriclayer can be mainly formed of SiO—ZnS, Si3N4, SiC, etc.; the functioninglayer can usually be formed of the one-off recording materials or theerasable recording materials, the one-off recording material usually canbe the dyestuff, such as dye, phthalocyanine, azo, etc., the erasablerecording material can be phase-change alloy or photochromic molecules.

In-between layer 115 is generally formed of transparent resin.Protecting layer 120 is mainly formed of UV cured lacquer. Protectinglayer 120 can be formed of the same material as substrate 110.

FIG. 2A to FIG. 2E are flow charts showing the manufacturing processesof optical disc 1 of the first embodiment. When manufacturing opticaldisc 1, firstly, pre-recorded groove 112 is formed on substrate 110 bymould-pressing; secondly, the surface of pre-recorded groove 112 insubstrate 110 is coated with first recording layer 114 which becomesundulate along pre-recorded groove 112; thirdly, first recording layer114 is coated with in-between layer 115 which will substantially filland level up the undulation on first recording layer 114 to make the topsurface of the in-between layer substantially flat and smooth; then, thetop surface of in-between layer 115 is coated with substantially flatand smooth second recording layer 115; and finally, protecting layer 120is further stuck and attached on substantially flat and smooth secondrecording layer 116, completing the manufacture of optical disc 1.

Aforementioned optical disc 1 is only an embodiment of the inventionOptical disc 1 has only two recording layers, in fact, second recordinglayer 116 can be coated with another in-between layer 117, as shown inFIG. 3; then the surface of in-between layer 117 is further coated withsubstantively flat and smooth third recording layer 118; and thenprotecting layer 120 is stuck and attached on the substantively flat andsmooth third recording layer so as to form three-recording-layer disc 1′as shown in FIG. 3. Similarly, four-recording-layer optical disc, evenfive-recording-layer or six-recording-layer optical disc can also bemade, thereby the multi-recording-layer optical discs can bemanufactured using a very simple method.

In the optical disc of the invention only one layer for recording thedata information becomes undulate, and other layers for recording thedata information are substantially flat and smooth, with which thein-between layer are coated directly and respectively, so that it isunnecessary that the stamper must be used once more when a new recordinglayer is required to be added on the optical disc, not only saving thestampers, but also increasing the productivity and reducing theproduction cost.

How to read the data information from and how to record the datainformation onto the optical disc of the invention will be describedwith respect to optical disc 1 according to the first embodiment of theinvention.

The method for reading the data information from optical disc 1according to the first embodiment of the invention is the same as thatused in the dual-layer optical disc in the prior art; and the method forrecording the data information onto first recording layer 114 having theundulate surface of dual-layer optical disc 1 is the same as that usedin the dual-layer optical disc in the prior art.

However, the method for recording the data information onto secondrecording layer 116 of optical disc 1 is different from the one forrecording the data information onto the dual-layer optical disc in theprior art. The reason is that the surface of second recording layer 116is flat and smooth, the address information can not be traced, so thatan optical device 2 similar to that as shown in FIG. 4 must be used torealize recording of data information.

In optical device 2 shown in FIG. 4, data laser beam A transmitted byfirst semiconductor laser device 21 passes through first collimatinglens 22, polarizing spectroscope 23, quarter-wave plate 24, double-tonespectroscope 25 and object lens 26 in sequence, then is reflected backafter reaching second recording layer 116 of optical disc 1, and thenreaches photo-electric converter 28 through detector lens 27. However,the surface of second recording layer 116 is flat and smooth, theaddress can not be traced, so that it is impossible to record the datainformation onto second recording layer 116 only by data laser beam A,therefore, service laser beam B is added in optical device 2 to assistdata laser beam A to record the data information onto second recordinglayer 116. Service laser beam B is transmitted by second semiconductorlaser device 31 which is on only when the data information is recordedonto substantially flat and smooth second recording layer 116, passesthrough holographic grating 32, second collimating lens 33, double-tonespectroscope 25 in sequence, and then passes through object lens 26along with data laser beam A, wherein service laser beam B is focused onfirst recording layer 114 to trace the address information on firstrecording layer 114 so as to assist data laser beam A incident on secondrecording layer 116 to record the data information onto second recordinglayer 116. When being reflected back, service laser beam B is deflectedto second photo-electric converter 34 through holographic grating 32.

When the data information has been recorded onto substantially flat andsmooth second recording layer 116, the address information can be storedby means of the physical change of second recording layer 116, so thatservice laser beam B is unnecessary when reading the data information.

While the present invention is described with reference to the specificembodiment, it is apparent for those skilled in the art to make somealternatives, modifications and changes according to above description.All of these alternatives, modifications and changes should be includedin the present invention when they fall in the spirit and the scope ofthe appendent claims.

1. An optical disc, comprising: a first layer, with its surfaceundulant, which includes material used to record information; a secondlayer, with its surface basically flat, which includes material used torecord information referring to the undulation of the first layer; andan in-between layer, which lies between the first layer and the secondlayer.
 2. The optical disc according to claim 1, further comprising asubstrate, wherein the first layer lies on the said substrate.
 3. Theoptical disc according to claim 2, wherein the said substrate haspre-recorded groove, the said first layer is undulant along thepre-recorded groove.
 4. The optical disc according to claim 1, furthercomprising a protecting layer, the said protecting layer covers the saidsecond layer.
 5. An optical disc manufacturing method, comprising thesteps of: (a) forming a first layer with its surface undulant on asubstrate, the said first layer includes material used to recordinformation; (b) forming an in-between layer on the first layer; (c)forming a second layer with its surface basically flat on the in-betweenlayer, the second layer includes material used to record informationrefer to the undulation of the first layer.
 6. The optical discmanufacturing method according to claim 5, wherein the said substratehas pre-recorded groove, and the first layer is undulant along thepre-recorded groove.
 7. The optical disc manufacturing method accordingto claim 5, further comprising forming a protecting layer on the secondlayer.
 8. An optical disc, comprising: a first layer, with its surfaceundulant, which includes material used to record information; a secondlayer, with its surface basically flat, adhering to the first layer,which includes material used to record information refer to theundulation of the first layer;
 9. The optical disc according to claim 8,further comprising an in-between layer, the said in-between layer liesbetween the first layer and the second layer.
 10. An optical discmanufacturing method, comprising: forming a first layer with its surfaceundulant on a substrate, and the said first layer includes material usedto record information; forming a second layer with its surface basicallyflat on the first layer, the second layer includes material used torecord information referring to the undulation of the first layer. 11.The optical disc manufacturing method according to claim 10, furthercomprising: forming an in-between layer, the said in-between layer lieson the first layer and the said second layer lies on the said in-betweenlayer.
 12. An optical disc recording method, comprising the steps of:recording the first layer of the optical disc; and recording the secondlayer of the optical disc referring to the first layer.
 13. The opticaldisc recording method according to the claim 12, wherein the surface ofthe said first layer is undulant and the surface of the said secondlayer is basically flat.
 14. An optical disc recording method, whereinthe optical disc has a first layer with its surface undulant and asecond layer with its surface mainly flat, the said optical discrecording method comprising the steps of: recording the first layer ofthe optical disc; and recording the second layer of the optical discreferring to the first layer.